1. Field of the Invention
The present invention relates to a device that prevents sticking of particles and restricts generation of particles. Particularly, the invention relates to a particle sticking prevention apparatus and a plasma processing apparatus that restricts generation of particles and prevents sticking of particles in a manufacturing process of semiconductors and flat display panels, for example.
2. Description of the Related Art
An environment in which manufacturing apparatuses of semiconductors or liquid crystal display units are installed has hardly any problem in cleanliness due to the advanced cleaning of clean rooms. On the other hand, particles that are generated within the manufacturing apparatuses have become a problem. In other words, it is required to prevent the sticking and generation of particles in the manufacturing process.
According to a conventional module that carries a substrate of a semiconductor or a liquid crystal display unit within a manufacturing apparatus, atmospheric air is introduced into the manufacturing apparatus via a fan filter unit (FFU) to remove particles which may be a cause of dust. Invasion by the particles is prevented in this way.
FIG. 1 is a schematic diagram of an atmospheric transfer module 10 of a semiconductor substrate in a general semiconductor manufacturing device. A carrying arm 2 supports and carries a semiconductor substrate 1 to a necessary position. A driving unit 3 moves and rotates the carrying arm 2 in the vertical and lateral directions. The atmospheric transfer module 10 is isolated by gate valves 4 from the outside or from another module such as a load lock chamber. The gate valves 4 are opened only when necessary. An FFU 5 that cleans air is provided above the atmospheric transfer module 10. The FFU 5 removes particles, that influence the semiconductor substrate or a device, from the air and introduces this air into a transfer chamber.
However, because the atmospheric transfer module 10 has a robot mechanism that carries the substrate, friction between an antifriction material and a member generates particles within the module. The FFU does not remove the particles that are generated within the device or the module. Further, particles or molecules having smaller diameters, that a filter cannot remove, enter a device. The particles generated within the device and the particles invading from the outside of the device receive an inertial force, gravity, and an electrostatic force, and move and are stuck to the semiconductor substrate. When a semiconductor substrate surface is polluted because of this sticking, inconveniences, such as a reduction in the production yield of a semiconductor device, occur.
In the load lock chamber adjacent to the atmospheric transfer module, particles are scattered and are stuck to the substrate in a nitrogen purge at the time of decreasing pressure from the atmospheric pressure or at the time of returning from vacuum to the atmospheric pressure. When an adiabatic expansion occurs due to a sudden drawing of a vacuum, moisture is frozen to generate particles. The generation or scattering of particles is conventionally avoided by decreasing an introduction speed of nitrogen gas. However, this lowers the total throughput of a device.
To overcome this difficulty, a cleaner disclosed in Japanese Patent Application Unexamined Publication No. 9-283597 is known. This cleaner sprays ionized air while a carrying arm is not used. The cleaner blows off particles that are stuck to the device due to static electricity or the like, and absorbs the particles on a filter. The ionized air is used to prevent charging of the carrying arm and to remove the charge from the surface of the arm.
On the other hand, in a plasma processing process for processing the substrate of a semiconductor device or a liquid crystal display unit, particles that are generated within the plasma processing unit cause problems.
In etching a semiconductor wafer that is positioned on a wafer stage within a vacuum processing chamber, gas is introduced from a gas shower head that is provided above the wafer. A high-frequency voltage is applied to between the wafer stage and the gas shower head. Electric power is supplied to the gas for the production of plasma, thereby producing a gas plasma. During this process, particles are generated, and these particles pollute the wafer.
When particles are stuck to the substrate, this causes a defect of a product which lowers a product yield ratio. In other words, particles that are stuck to the substrate form a mask which disables the etching device for etching a film. A particle that is stuck to the substrate forms a nucleus which causes an abnormal growth of a film in a film producing device. These particles are generated when reaction products stuck to the inside of a processing unit peel off from the internal surface of the unit for some reason. Means for effectively preventing peeling off and scattering of these particles are demanded.
In order to prevent particles falling onto the substrate, Japanese Patent Application Unexamined Publication No. 7-58033 proposes a device that has an openable and closable shutter which covers the substrate after the process ends.